1. Field of the Disclosure
The present disclosure relates to a mobile device, and more particularly to a mobile device that performs wireless communication with a vehicle-mounted device.
2. Description of the Related Art
Presently, a system, called a keyless entry system, is in use. The system includes a vehicle-mounted device, which is mounted in a vehicle, and a mobile device, called an electronic key, carried by the user of the vehicle. According to a result in wireless communication between the vehicle-mounted device and the mobile device, the system allows a door of the vehicle to be locked or unlocked, allows the engine to be started, and performs other tasks.
The mobile device used in the keyless entry system includes a circuit board on which an electronic circuit used to perform wireless communication with the vehicle-mounted device is mounted, a battery holder that holds a battery from which electric power is supplied to the electronic circuit, and a case member in which the circuit board and battery holder are accommodated. On the front surface of the circuit board, test ports are usually provided that are test terminal electrodes used to inspect the performance of the electronic circuit before the mobile device is shipped as a product.
An example of a conventional mobile device used in this type of system is described in Japanese Unexamined Patent Application Publication No. 2013-100657. The structure of the conventional mobile device described in Japanese Unexamined Patent Application Publication No. 2013-100657 will be described with reference to FIGS. 10A and 10B. FIGS. 10A and 10B illustrate the structure of the conventional mobile device, which is a card key 301 (mobile device) described in Japanese Unexamined Patent Application Publication No. 2013-100657.
As illustrated in FIGS. 10A and 10B, the card key 301 is a mobile device shaped like a card. It includes a card key main body 310, which is the main body of the card key 301, and an ornament 322 with a vehicle manufacturer and a model indicated on the surface 322a of the ornament 322. The card key main body 310 includes a circuit board 340 on which an electronic circuit used to perform wireless communication is formed and also includes a molded resin 313 (case member) in which the circuit board 340 is accommodated. A recess 311 into which the ornament 322 is fitted is formed in the vicinity of the center of a surface 310a of the card key main body 310. A battery space 312 (battery holder) in which a battery 323 of a button type is installed is provided at an end of the card key main body 310.
An electronic part (not illustrated) is mounted on the circuit board 340, forming an electronic circuit used for wireless communication. A plurality of test points 331 (test ports), which are test terminal electrodes, are formed on the surface 340a (one of the plate surfaces) of the circuit board 340. The test points 331 are disposed at the position at which the recess 311 in the card key main body 310 is formed, so a test probe or the like can be brought into contact with the test points 331 before the ornament 322 is fitted into the recess 311 to check the performance of the electronic circuit.
A battery terminal 341, a battery terminal 342, and a plurality of lands 361 are accommodated in the battery space 312. The battery terminal 341 is an electrode that comes into contact with the surface 323a (electrode surface) of the battery 323 on the positive electrode side when the battery 323 is installed. The battery terminal 342 is a ground electrode that comes into contact with the surface 323b (electrode surface) of the battery 323 on the negative electrode side when the battery 323 is installed. The lands 361 are electrodes that come into contact the surface 323b of the battery 323 on the negative electrode side when the battery 323 is installed. The lands 361 are connected to their corresponding test points 331. After the battery 323 is installed in the battery space 312, a battery cover 321 is attached around the battery space 312 so as to cover the battery 323.
The card key 301 is structured as described above. With the card key 301, when the card key 301 is used with the battery 323 installed in the battery space 312 (simply referred to below as “when the card key 301 is used”), the surface 323b of the battery 323 on the negative electrode side comes into contact with the battery terminal 342 and lands 361, causing the test points 331 to be grounded. Since the test points 331 are grounded when the card key 301 is used, it is prevented that static electricity enters the electronic circuit from the test points 331.
The case member where a mobile device is made of a synthetic resin or another material through which electromagnetic waves can easily pass so that wireless communication with a vehicle-mounted device is not interfered. Test ports are provided so as to be exposed to the surface of a circuit board, and need to have a large size to a certain extent so that a test probe can be easily brought into contact with the test ports. Accordingly, electromagnetic wave noise that has intruded from the outside of the mobile device can easily enter the test ports. This has been problematic in that, if no countermeasures against noise are taken, the electromagnetic wave noise that has entered the test ports may be transmitted toward the electronic circuit and the electronic circuit may thereby be adversely influenced.
The adverse influence of electromagnetic wave noise on the electronic circuit is further increased if the test ports are disposed near wiring electrodes connected to an electronic part such as an IC chip. However, this type of mobile device is required to be compact so as to be easy to carry. Therefore, the test ports are often disposed near wiring electrodes connected to an electronic part, in which case countermeasures against noise have been particularly important.
In view of this, the test points 331 (test ports) of the card key 301 (mobile device) described in Japanese Unexamined Patent Application Publication No. 2013-100657 are grounded when the card key 301 is used so that it is possible to suppress the electromagnetic wave noise that has entered the test points 331 from the outside of the card key 301 from being transmitted toward the electronic circuit. In the structure described in Japanese Unexamined Patent Application Publication No. 2013-100657, however, the transmission of the electromagnetic wave to the test ports can be suppressed only when all tests ports can be grounded while the mobile device is in use. Therefore, if the circuit board includes a test port that cannot be grounded while the mobile device is in use, such as, for example, a test port that is electrically connected to a switch element used for an input operation, it is not possible to suppress the adverse influence of electromagnetic wave noise that has entered the test port from the outside of the mobile device.